Method of manufacturing chromium of chromium alloys



a ted M r. 13, 1934 I 1,951,091

UNITED STATES PATENT OFFICE METHOD OF MANUFACTURING -CHROMIUM F CHROMIUM ALLOYS Ture Robert Haglund, Stockholm, Sweden No Drawing. Application January 23, 1933, Serial No. 653,185. In Sweden August 22, 1932 7 Claims. (Cl. 75-48) This invention relates to processes of manucomplete oxidation. Generally, it is, however. facturin'g chromium or chromium alloys, such as more suitable to oxidize partly the chief part or ferro-chrome low in carbon and chromium-althe chromium alloy or the whole alloy so that loyed iron and steel, in an electric furnace in the particles of chromium alloy to be supplied which a refining action is obtained by means of to the slag bath are coated by a shell of chro- 60 a molten slag-bath containing chromium oxide, mium oxide. Such particles do not attractthe and especially to such processes in which chroelectric current flowing from the electrodes to miferous material is successively supplied to the the slag bath a d accordingly Vo a o eslag bath in the form of a pulverized chromium tallic chromium is avoided which otherwise takes alloy high in carbon, fori'nstance a pulverized place by the direct action of the electric cur-'65 ferro-chrome containing to 75% Cr and 6 to rent or the electric are on alloy particles having 10% C. A process of this kind is described in clean metallic surfaces. Furthermore, the curmy copending application Ser. No. 632,865 filed rent flow will be. more quiet when using an al- September 12, 1932. Said application describes loy the particles of which have a protecting sur- 15 a process for 'decarburizing chromium alloys by face layer of oxide and the absorption of nitroreaction with a slag bath having a high content gen in the alloy which easily takes place when of chromium oxide and being heated by means an electric arc is playing against non-oxidized of electrodes, operating in electrical connection surfacesof the chromium alloy particles, will also with the top portion of said slag bath, fine parbe avoided. I

go ticles of a chromium alloy high in carbon being The roasting or oxidation ofthe ferro-chrome successively added to the slag bath and spread is carried differently far, dependent on the alloy therein on account of the stirring action caused to be manufactured. If a ferro-chrome with a by the carbon monoxide evolved in the slag by the content of carbon less than 0.5% shall be manureaction between the chromium oxide of the slag factured a degree of oxidation amounting to 15 to 9,5 and the carbon of the added particles of chro- 40% should be used, whereby it will be possible to so mium alloy. maintain a chromium oxide content in the slag The chief object of the invention is-to mainbath of about 50 to CrzOs. In manufacturtain a high content of chromium oxidein the ing chromium-alloyed iron, for instance of the slag bath during the whole operation, thus farustless qualities, it is possible to work with escilitating the refining action on the chromiferous sentially lower degrees of oxidation, for instance material supplied to the slag bath. between 5 and 15%, and even lower, as the v According to the invention the chromium alloy composition of the slag bath in such case, can be is more or less completely roasted or. oxidized beregulated also in other manner, for instance by fore it is supplied to the slag bath. In this manadditions of iron ore. Additions of other alloy- 35 ner a material rich in chromium and chromium ing metals, for instance nickel, can in such case oxide but substantially free from other oxides, be supplied either tov the metal in the electric such as aluminium and magnesium oxides, havfurnace or partly or wholly after the tapping of ing a diluting action on the slag, is supplied to the alloy from the electric furnace. In manuthe slag bath, whereby the latter in spite of the facturing chromium-alloyed iron or steel an ad- 0 reducing action of the carbon of the chromium justment of the percentage of chromium of the alloy, can be maintained at a high percentage alloy produced can also be effected by adding of chromium oxide during the whole refining ierr'o-chrome low in carbon after the alloy has operation. been tapped from the furnace.

It is, however, possible to supply a part of the The roasting or oxidation of the chromium 5. chromium oxide required for the process in the alloy may be performed by means of atmospheric form of chromium ore or to produce a part of air, oxygen, steam or other oxidizing agent and the chromium oxide by oxidation of apart of is carried out, preferably, at temperatures be- 1 the metallic chromium in connection with the tween 1200 and 1400 C. In some cases, especially refining operation, for instance by additions of when arelatively low degree of oxidation is aimed 5 =ir0n ore. Y at, a considerably lower temperature can be used,

It is not'necessary to preoxidize all chromium for instance down to 900 C. The roasting of the 1 alloy usedas charging material in carrying out pulverized ierro-chrome may be 'facilitated by the process as itwill be sufficien to oxidize only mixing it with other substances having a-loosena part thereof, in which case the oxidation, howing action thereon or which promote the forming 56 ever, is ca comparatively if desired to or, chromate, for instance limestone or quicklime. An addition or 1 to 2% C90 will be suflicient for such purpose. Suitable furnaces for the performance of the roasting operation are, for instance, channel furnaces, rotary furnaces 5 and down-draft pans otherwise used in sintering fine ores. The oxidation process has also a decarbonizing action on the chromium alloy. For instance, at a roasting carried out at 1200 C. to an oxidation degree of a decarbonizing amounting to more than has been noted.

The chromium alloy used as starting material should havea low percentage of silicon, preferably less than 1%. The most favorable results have been-obtained with chromium alloys con- 5 taining only one or some tenths of a percent of What I claim is:- 1. In a method of manufacturing chromium or chromium alloys by melting and refining a 'l carbonaceous chromium alloy in a molten slag bath containing chromium oxide, the step which consists in partially oxidizing the chromium content of the alloy before adding it to the slag bath. 7

" '2. A method of manufacturing chromium alloys low in carbon, which comprises roasting ferro-chrome high in carbon to partially oxidize its content of carbon and partially oxidize its content of chromium, and then melting and refining 9 the roasted ferro-chrome in a molten slag bath containing chromium oxide.

3. A method as claimed in claim 1, in which a molten slag bath containing chromium oxide.

the chromium alloy is pulverized and then roasted to an oxidation degree of 5 to 40%. Y 4. A method as claimed in claim 1, in which a chromium alloy low in silicon is roasted to partially oxidize its content of chromium and then melted and refined in a molten slag bath containing chromium oxide.

5. A method of manufacturing chromium alloys low in carbon, which comprises roasting ferro-chrome high in carbon to partially oxidize its content of chromium in presence of a basic ,substance which promotes the formation of chromate in the roasting operation, and then melting and refining the roasted ferro-chrome in 8. A method of' manufacturing chromium alloys low in carbon, which comprises roasting ferro-chrome high in carbon to partiallyoxidize its content of chromium in presence of a basic substance, and then melting and refining the roasted ferro-chrome in a molten slag bath containing chromium oxide.

'1. In a method of manufacturing chromium on chromium alloys by melting and refining a chromium alloy having a high content of carbon by means of a molten slag bath containing chromium oxide,.the step which comprises adding the chromium alloy at least partially in the form of small particles having a skin of chromium oxide on their surface. TURE ROBERT HAGLUND. 

